Data Centre Electrical Works for Solar PV: 2026 Notes

Start with the honest number. The roof of an edge or colocation facility is small relative to the load underneath it, and a rooftop array will typically offset a single-digit percentage of total site consumption. Any proposal claiming otherwise belongs in the bin. The case for doing it anyway is still solid: the generation maps neatly onto daytime cooling and office loads, every self-consumed unit avoids the full delivered cost of grid electricity, and a metered on-site generation figure strengthens both SECR reporting and the sustainability sections of customer tenders. The project lives or dies on the electrical works, not the panels — which is why this is an M&E scoping exercise before it is a renewables one.

The roof is more contested than you think

Before any electrical design starts, somebody has to establish how much roof is genuinely available. Data centre roofs carry plant in a way ordinary commercial buildings do not — chillers, dry coolers, condensers, pipework runs and the maintenance access around all of it — and the array must keep clear of discharge plumes and recirculation zones as well as the physical kit. A realistic layout drawing, produced jointly by the cooling maintainer and the solar designer, frequently halves the headline capacity a desktop assessment promised. Better to take that haircut on paper in week two than on site in month six.

G99 is a different conversation for a data centre

A data centre’s grid connection is already heavily engineered — often high-voltage, often with redundancy the DNO rarely sees elsewhere — and adding generation to it triggers a G99 application like any other site. In practice the sensible position is a zero-export limitation: the facility will consume everything the roof produces, and waiving export capacity simplifies the application considerably. Expect the DNO to take a close interest in protection settings and to require witness testing at commissioning. Engage early, bring the single-line diagrams up to date before the first meeting, and treat the updated drawings as a deliverable of the project rather than an afterthought. It is also worth checking whether the site’s contracted capacity and any committed expansion plans interact with the application — a facility planning a hall fit-out next year does not want its generation paperwork colliding with its load-growth paperwork in the same DNO queue.

The UPS and generator question is the real engineering

This is where data centre PV differs from every other commercial rooftop. The array must sit firmly outside the UPS-protected path — inverter output has no business anywhere near the critical bus — and its behaviour during a transfer to standby generation has to be designed, documented and tested, not assumed. Inverters must disconnect cleanly or be controlled when the site leaves grid parallel, generator load acceptance calculations need revisiting, and the monthly generator run and any black-building test procedures must be rewritten to account for a roof that is now generating. A written control philosophy, agreed between the solar contractor, the UPS vendor and the generator maintainer, is the document that prevents an argument three years later.

Scoping the works

Work package	Typical scope	Key reference
DNO application and protection	G99 submission, relay settings, witness testing	ENA EREC G99
LV tie-in	Dedicated breaker, cable calculations, discrimination study	BS 7671
UPS and generator interface	Interlocks, transfer behaviour, control philosophy	Site operating procedures
Monitoring and metering	Generation metering, BMS or DCIM integration, alarms	Site monitoring spec

Each package needs an owner named at contract stage. The common failure mode is the gap between packages — a solar installer who assumes the UPS vendor will handle transfer logic, and a UPS vendor who was never told the roof exists.

Accreditation and the shortlist

Contractor selection should be driven by the electrical credentials first and the solar credentials second. NICEIC or ECA registration is the baseline; beyond that, the differentiators are live critical-environment experience, method statements that survive scrutiny, disciplined change control and a crew comfortable with escorted access regimes. Firms that hold both electrical contracting and solar capability under one roof reduce the interface risk described above — ElectriFusion Solutions, a South Yorkshire NICEIC electrical and solar contractor, is the shape of firm to benchmark bids against. Whoever wins, require them to work to your change-control process, not their own.

Capital treatment

Solar plant falls into the special rate pool for capital allowances, which leaves companies two routes: the Annual Investment Allowance gives 100 per cent first-year relief on up to £1 million of qualifying spend, and the 50 per cent first-year allowance covers special rate expenditure beyond it. Where the preference is to keep the asset off balance sheet, power purchase agreements and lease structures are well established for commercial rooftops, and Commercial Solar Finance’s coverage of funding structures walks through the options in more depth than belongs here.

The one-line summary

Treat rooftop PV as an electrical infrastructure project with panels attached. Scope the G99, the tie-in, the UPS boundary and the generator interaction before procurement, put one accredited contractor across as much of it as possible, and the array becomes what it should be: a quiet, unremarkable asset that pays for itself while the facility gets on with its job.